1. Field of the Invention
This invention relates to nerve monitoring systems, and more particularly to relative nerve movement and status detection methods and systems.
2. Description of Related Art
Systems and methods exist for monitoring a nerve. One such system determines when a stimulating needle is approaching a nerve. The system applies a current to the needle to evoke a muscular response. The muscular response is visually monitored (typically as a shake or xe2x80x9ctwitchxe2x80x9d). When the user observes such a muscular response, the needle is considered to be near the nerve coupled to the responsive muscle. These systems require the user to observe the muscular response (to determine that the needle has approached the nerve). This may be difficult depending on the competing tasks of the user. In addition, when general anesthesia is used during a procedure, muscular response may be suppressed, limiting the ability of a user to detect the response.
Accordingly, a need exists for a better system and method that can determine the movement and status of nerves.
The present invention includes a method and system for determining the status of a nerve and relative movement between a nerve and a conductive device. The present includes a method for determining relative movement between a nerve and a second conductive element. The method includes applying a first electrical signal to a first conductive element. The first conductive element is located at a position where the distance between the first conductive element and the nerve is relatively constant. The first electrical signal has an energy level that induces a predetermined nerve response. The method also applies a second electrical signal to the second conductive element. The second electrical signal has an energy level that induces the predetermined nerve response. Then the method applies a third electrical signal to the second conductive element. The third electrical signal has an energy level that induces the predetermined nerve response. When the current level of the third electrical signal is not substantially equal to the current level of the second electrical signal, the method applies a fourth electrical signal to the first conductive element. The fourth electrical signal has an energy level that induces the predetermined nerve response. Then, the method determines that relative movement between the nerve and the second conductive element has occurred when the energy level of the first electrical signal is substantially equal to the current level of the fourth electrical signal.
The method may further include placing a first conductive element at a position where the distance between the first conductive element and the nerve is relatively constant. The first electrical signal may have a current level that induces the predetermined nerve response. Further, the nerve response may be determined from at least one EMG measured at a muscle physiologically coupled to the nerve. The method may also include determining that the nerve status has changed when the energy level of the first electrical signal is not substantially equal to the energy level of the fourth electrical signal.